The use of solar cells is becoming widely used as a measure to tackle the global environmental issues. By virtue of the abundant resources and high efficiency of photoelectric conversion, majority of the solar cells are manufactured by using silicon crystals. Among them, production of solar cells using polycrystalline silicon substrates manufactured by electromagnetic casting method is increasing.
In this method of electromagnetic casting of silicon, as shown in FIG. 5, a copper crucible 200 in which a coolant is circulated and an induction coil 300′ arranged on the outer surface of the copper crucible 200 are used in a furnace vessel 100 to levitate a silicon mass S in the copper crucible 200 under the electromagnetic force and the silicon mass S is solidified by continually pulling it downwards thereby to obtain a cast silicon ingot.
Accordingly, since the levitation melting of the silicon mass S is carried out in the copper crucible 200 using electromagnetic force, molten silicon S′ does not come into contact with the inner surface of the crucible 200, whereby the contamination of the molten silicon S′ by impurities coming from the crucible 200 can be avoided. Also, since the crucible 200 used for levitation melting of the silicon mass S does not come into contact with the molten silicon, the crucible is not damaged and can be used permanently.
Thus, the silicon electromagnetic casting mentioned above has become one of the commercial manufacturing methods which provides a high productivity by manufacturing long silicon ingots continuously, high quality and homogeneity by virtue of stable and regular casting conditions.